The present relates to a reproduction machines and in particular to fuser belts for use in photocopy and related printing art equipment.
In the photocopy and related printing arts, systems must be designed to transport the media upon which an image is printed. These transport systems must reliably maintain the geometric stability of the media throughout the photocopy or printing process. This becomes increasingly difficult when the media sheets are in a wider format, such as in engineering copy applications. Further, it is more difficult to maintain the geometric stability of the media as the throughput rate increases and the fusing temperature increases. Under such conditions, in particular, it is difficult to keep media with a high moisture content, such as paper, from wrinkling and puckering during the fusing or heating process.
These media deformations occur when water vapor is expelled from the media during the high-temperature fusing process. A portion of the water within the media is turned to steam during the fusing process. Some of this steam is trapped within the media thereby forming gas pockets between the fuser belt and the heated roller. The gas pockets are randomly located and adversely affect the transfer of thermal energy away from the media. Cooler regions of the media become depositories for water vapor expelled from the hotter regions of the media. These temperature and moisture gradients cause deformation of the media, such as puckers and wrinkles. Further, these gradients and resultant deformations may cause regions of poor image fusing and image deterioration.
Copy media based on plastics, such as drafting film, deform and transport poorly if too much thermal energy is transferred into the media during the fusing process because the higher temperatures cause the material to soften and lose its strength. If the beam strength of the media is lowered too much before it exits the fuse, the media will usually buckle and cool in an objectionable non planar form.
The prior art has dealt with these concerns by using expensive precision-made fuser belts and controlled transport geometry. Additionally, the prior art uses belt fusers with high nip pressures generated by smooth-surfaced belts operating under high tension so as to press the media tightly against the heated roller. The resulting pressure eliminates the tendency of gas pockets to form in the media as the media is pressed between the fuser belt and the heated roller. The high tension in the fuser belt requires that the fuser belt drive mechanism use rollers having very high bending movements which in turn requires that the rollers be large, heavy and expensive to manufacture and to operate.
Prior art fuser belts have smooth surfaces which have high area of contact against the heated roller. This contact allows thermal energy to be transferred to the fuser belt and the rollers upon which the belt is located. This transfer of thermal energy is undesirable because it causes the warm-up time of the fuser to be long.
The thermal energy stored in the belt and the belt support rollers will eventually be transported into the side of the media opposite from the heated roller. This extra thermal energy introduced into the media adversely affects its paper handling performance. When the media is paper, wrinkle and pucker may occur. When the media is vellum, stalling may occur. When the media is film, softening is excessive. The film loses its internal strength causing puckers, wrinkles and image deformation. Prior art fuser systems require the use of the expensive thick film media.
In view of the above, it is the principal object of the present invention to provide a fuser belt for reproduction machines which allows water vapor to escape from the media during the fusing process without deforming the media.
It is a further object of this invention to provide a fuser belt which can be operated with a low belt tension thereby avoiding the need for high roller bending moments. This, in turn, allows the use of small, light-weight rollers of low thermal mass.
It is a further object of this invention to provide a fuser belt which removes thermal energy from the heated roller at a rate substantially reduced over that of the prior art thereby reducing the deformation of media such as film and to improve media handling and transport.
Still another object is to provide a fuser belt which can be incorporated into conventional reproduction machines with none or little retrofitting.